Effect of sand properties on casting defect

Abstract

Blow hole, pin hole and shrinkage cavities are most common defect found in cast steel factories in Thailand. Various factors contributed to these defects in CrMo40L low alloy steel were investigated. Sand properties and pouring temperatures were considered to be two major factors. Sand properties and pouring temperature data recorded during actual casting operation in a factory were analyzed with respect to the defects found in cast products. Experimental design was applied to determine the number of experiments to simulate actual casting condition. Appropriate levels of sand mixing were chosen to vary permeability, compressive strength, and % loss on ignition. The levels of sand mixing were controlled by clay content as 4.5 and 6.5%. moisture as 2.5 and 4% starch content as 0.5 and 1% AFS grain finess number of sand as 46 and 49 and pouring temperature of 1550 ℃ and 1620 ℃. The cavities occurrence was measured by stereological measurement. The result of measurement led to comparisons of each factor on the cavities occurrence using statistical analysis. The best condition that minimizes gas cavity is grain finess number of 46. clay content of 4.5%. starch of 0.5%. moisture of 2.5% and pouring temperature of 1620 ℃. This same sand formula can also be used in accompanied with pouring temperature of 1550 ℃ in order to save cost. However, the low pouring temperature is not recommended for pouring to a lot of molds by single ladle because of the effect of temperature drop and the greater chance of blowhole.